Pipes that contain and transport water are used in numerous applications, which are generally divided into the broad categories of non-pressure and pressure applications. The present invention is useful for pipes suitable for both non-pressure and pressure applications, and is particularly usefil in sewage and drain pipes. Other applications for the present invention are also contemplated, such as conduit sections used for housing telecommunications cable, fiber optics cable, and electrical wire or cable.
Pipe can be installed in a number of ways, one of which is the traditional pipe laying technique of simply digging a trench and then placing the pipe sections in the trench, assembling the sections into a pipeline and then covering the pipeline. There are also trenchless pipe installation methods known as microtunneling, sliplining, and pipe bursting, which are described below. The present invention can be used in traditional applications, and is particularly useful in trenchless applications.
Microtunneling is a process in which a vertical access shaft is excavated to the pipe's starting grade. The term starting grade means the level or depth at which the pipe will be installed. A second vertical access shaft is constructed at the ending location for the pipeline. The pipeline is installed between the two vertical shafts. A microtunneling machine, which is usually a remotely controlled, steerable, boring machine having a cutter head at one end, is lowered into the first access shaft. The microtunneling machine bores or cuts through the wall of the shaft and the cutter head drills a tunnel through the soil towards the second access shaft. The soil that is displaced by the cutter head is removed either by an auger system, by which the soil is mechanically removed from the hole, or a slurry system, which uses water to flush the loose soil from the hole.
Before the entire microtunneling machine exits the access shaft and enters the tunnel, a pipe section is attached to the rear of the machine. Axial compressive force or pressure, directed along the longitudinal axis of the pipe section, is applied to the end of the pipe section opposite the machine. This force pushes the machine forward, with the pipe section attached, into the tunnel towards the second shaft. A second pipe section is attached to the first, then a third is attached to the second, and so on. This process of adding additional pipe and pushing the machine forward continues until the machine enters the second access shaft. At that point, an entire length of pipe, consisting of a plurality of pipe sections, exists between the access shaft and the second shaft. The machine is then disconnected from the pipe and the pipeline is complete.
During the tunneling process, the machine is advanced forward by pushing against the end of the last pipe section attached and transmitting the axial compressive force through the connected pipe sections. Therefore, the pipe sections must be joined in a manner such that a significant amount of axial compressive force can be transmitted through the joints without buckling or otherwise damaging the joints or the pipe sections. Furthermore, the tunnel formed by the microtunneling machine is preferably just slightly larger than the diameter of the pipe because the larger the diameter of the tunnel, the greater the chance that the tunnel will collapse. If the pipe joints include sections that project outward from the diameter of the pipe wall, a larger tunnel must be bored to accommodate the pipe joints, thereby creating a greater risk that the tunnel will collapse. Therefore, it is important that the pipeline have a smooth outer surface.
Sliplining is a method of rehabilitating deteriorated pipelines by inserting a new, smaller diameter pipe, called a slipliner pipe, inside of an existing larger-diameter pipe. When sliplining, an access pit is dug to an existing pipeline, the access pit being slightly longer than the length of one section of the slipliner pipe. The top half of the section of existing pipe is exposed at the bottom of the access pit, and is removed leaving the bottom pipe half, known as a pipe cradle. A slipliner pipe section is then placed inside the pipe cradle and is pushed into the existing pipe, parallel to the longitudinal axis of the existing pipe. A second slipliner pipe section is then lowered into the pipe cradle and joined to the first section. The second pipe section is then pushed into the existing pipe causing the first pipe section to advance further into the existing pipeline. Additional pieces of pipe are joined, and the assembled pipe is advanced until the existing pipeline is completely sliplined or until the next access pit is reached. When the sliplinig is complete, grout or other sealing material is pumped into the gap between the existing pipe and the new pipe along the entire length of existing pipe that was sliplined.
Often, the existing pipe to be sliplined is broken and dilapidated. The existing pipe's joints are sometimes separated, and pieces of debris or sections of the existing pipe extend into the pipe cavity creating obstructions. Furthermore, if the slipliner pipe were to have flared or wide joints, the slipliner pipe inserted into the existing pipe will have a relatively small diameter as compared to the existing pipe and therefore may not be capable of transporting a large enough volume of liquid. Therefore, it is important that a slipliner pipe have a smooth outer surface. Additionally, slipliner pipe sections also must be capable of efficiently transferring an axial compressive force from one slipliner pipe section to another without buckling or failing at the pipe joint.
Pipe bursting is another method of pipeline rehabilitation in which the existing pipe is replaced by a pipe having a diameter equal to or larger than the existing pipe. In this method, access is first gained to an existing pipe through a manhole or access pit. A small diameter steel pipe is inserted through the existing pipeline to a second access location. A pipe bursting head, which is generally a solid metal cone, is then attached to the steel pipe at the second access pit. The steel pipe with the pipe bursting head is then retracted towards the first access location by pulling the steel pipe. As the bursting head is pulled through the existing pipe, the existing pipe bursts into pieces that are displaced into the soil. A new pipe is pulled behind the pipe bursting head and creates a new pipeline. Pipe bursting creates numerous snags or obstructions, which are usually pieces of broken existing pipe. Therefore, it is important that the outer surface of the new pipe be smooth and have no projections.
A joint for use in the applications described above is disclosed in commonly-assigned U.S. Pat. No. 5,547,230, which is incorporated here by reference. The joint disclosed therein generally solved the problem of providing a substantially smooth outer surface in a pipeline made up of pipe sections having a variable wall thickness. It has proven successful for use in many microtunneling, sliplining, and pipe bursting applications. The present invention is an improvement over the joint disclosed in the '230 patent and is particularly suited for applications in which axially compressive and tensile forces are unusually great.
Many prior-art joint structures have a propensity to fail when exposed to unusually high, axial compressive forces often associated with microtunneling, sliplining, and pipe bursting, as well as tensile forces encountered during use that would tend to pull the joint apart. When exposed to those forces, joints have had a tendency to fail. In particular, prior-art joints contain a small gap that, generally, has faced the inner diameter ("ID") to achieve a smoother outer wall. When unusually high compressive forces are applied, the pipe and corresponding pipe joint have a tendency to buckle outward. When the gap faces the ID, there is no mechanism or structure to contain outward buckling. Thus, pipe joints have failed due to outward buckling of the joint when exposed to unusually high axial compressive forces, or the pulling apart of the joint when exposed to strong tensile forces.
Prior-art structures on occasion also have encountered problems with installation and repair. When the compressive forces are applied, the gaskets can slip or deform out of place, thereby preventing an adequate water-tight seal at the joint.
The present invention solves these and other problems associated with prior-art pipe joints.